This invention generally relates to fasteners, and, particularly, to a nut having an improved structure allowing quick insertion of a threaded bolt and removal thereof.
The prior art has shown various structures for threaded fasteners, such as an internally threaded nut, which may be quickly attached to an externally threaded member such as a bolt, screw or stud, without the time consuming need to rotate the nut a great number of revolutions on the externally threaded member. As illustrated in U.S. Pat. Nos. 3,695,139, 4,378,187, or 5,324,150, fasteners of the quick connecting type generally have an internally threaded nut formed with two or more segments or shells which separate to allow an externally threaded member (bolt) to be pushed into the threads, then close together for tightening over fewer thread pitches on the bolt than would normally be the case with a solid nut. There is typically a frusto-conical surface at the front side (toward the bolt) inside the body of the nut casing to force the segments or shells inwardly for tightening, this surface being at a large angle relative to the axis of the nut. Additionally, some prior devices employ a second frusto-conical surface at the rear of the nut casing and corresponding conical surfaces formed on the threaded segments for spreading or separating the segments when a bolt or the like is inserted.
In U.S. Pat. No. 5,340,252 to Weddendorf, a quick connect fastener has a nut formed with a plurality of internally threaded shells having small-angle frusto-conical external surfaces abutting and cooperating with an internal frusto-conical surface at a front end of the nut casing (smaller-diameter end facing toward the position of an externally threaded bolt). The shells include annular internal grooves at the front and rear sides thereof for receiving spring clips which have a C-shape and are snapped into the respective grooves. The spring clips bias the shells radially outwardly, tending to separate them, i.e., to spread them apart, and thus urge the conical external surfaces of the shells against the conical internal surface of the nut casing, and thus urge the shells rearwardly along the surface of the nut casing toward its larger diameter end. A coil spring is disposed within the nut casing at the rear (larger-diameter) end abutting the rear ends of the shells and urging them forward toward the front end. Prior to use, the coil spring overcomes the opposing force of the spring clips and holds the shells against a stop at the front end of the nut casing. When the bolt is pushed into the smaller-diameter end of the nut casing (or vice versa), the shells are driven away from the stop at the front end of the casing and are urged radially outwardly by the force of the clips. The inside threading diameter of the shells is thereby increased to allow the bolt threads to push past the internal nut threads. When the pushing force is released, the shells are urged toward the front end of the nut casing by the coil spring and are forced radially inwardly by contact of the conical external surfaces of the shells with the conical interior surface of the nut casing. As the shells are moved toward the front end, they are urged radially inward and their internal threading then engage with the external threading of the bolt, and the nut can be increasingly tightened on the bolt in a small number of turns.
However, the quick connecting nut assemblies of the prior art, such as shown in U.S. Pat. Nos. 3,695,139, 4,378,187 and 5,324,150, employ a relatively large taper angle in the nut casing in order to facilitate the spreading apart of the shells when a bolt is inserted. However, the large taper angle provides contact against the external surfaces of the shells for tightening them only near the front end of the nut casing. This means that the forces on the threads of the shells, after the system is preloaded, have a weaker load path to ground (or the casing) which reduces the strength of the fastener assembly. While the nut assembly in U.S. Pat. No. 5,340,252 employs a smaller taper angle for greater tightening force, it requires the use of the C-shaped (expansion) spring clips at both ends to spread the shells when a bolt is pushed into the assembly, and the coil (compression) spring at the rear to overcome the force of the C-shaped spring clips to urge the shells back toward the front end of the nut casing for tightening down.
A principal object of the present invention is to provide a quick insertion fastener with an improved configuration of shell assembly that allows quick insertion of a threaded member and tightening (preloading) with a small number of turns, while also ensuring a distributed contact between the shell assembly and the nut casing to increase the strength of the fastener assembly. The shell assembly is designed to perform its function effectively while avoiding the need for multiple parts, multiple springs, and a complex assembly. A further object of the invention is to also provide a means for quick removal of the fastener.
In accordance with the present invention, a quick insertion fastener has an internally threaded first member adapted to be quickly attached and tightened on an externally threaded second member inserted therein. The first member is formed with: (a) a casing having an internal surface at a front part thereof in a frusto-conical shape with a taper angle xe2x80x9cxcex1xe2x80x9d, said front part of the casing being oriented toward the second member for insertion thereof; (b) a plurality of shell segments radially arranged on a fastener axis to form a displaceable shell assembly contained in said casing, each of said shell segments having a similar shape with an external surface at a front end thereof tapered in a frusto-conical shape with a taper angle xe2x80x9cxcex1xe2x80x9d corresponding to the taper angle of the internal front surface of said casing and internal threads having a thread height xe2x80x9chxe2x80x9d and pitch xe2x80x9cpxe2x80x9d; (c) a spring member positioned at a rear part of said casing which is arranged to provide an elastic force to elastically retain rear ends of the shell segments to be axially movable in said shell assembly; and (d) an end retainer provided at the rear part of said casing having a taper for engaging the rear ends of the shell segments and displacing them radially as they are moved axially toward the end retainer such that the shell segments are spread apart radially to allow insertion of the second member past the internal threads of the shell segments when the shell segments are pushed axially by the force of insertion of the second member into the front part of said casing and toward the end retainer at the rear part of said casing.
The shell assembly is configured such that when the second member (e.g., a bolt) is inserted with an insertion force into the front part of the first member (e.g., a nut), the shell assembly is displaced axially toward the rear part of the nut casing by a distance xe2x80x9cxcex4xe2x80x9d which is equal to h/tan(xcex1/2), and the shell segments are moved apart radially by a distance xe2x80x9chxe2x80x9d against the elastic force of the spring by the taper of the end retainer. This allows the internal threads of the shells to clear the thread height xe2x80x9chxe2x80x9d and allow the external threads of the bolt to be inserted past the internal threads of the shell segments without interference. When the insertion force of the bolt is released, the spring member urges the shell segments together, and the internal threads of the shell assembly become engaged with the external threads of the bolt, so that the nut can now be tightened with a small number of turns on the bolt.
In a preferred embodiment, the spring member is constituted by a radial spring or O-ring that holds together flanges extending from the rear ends of the shell segments, and the end retainer has a tapered annular collar which engages the flanges of the shell segments. As the shell assembly is displaced axially under the insertion force of the bolt, the shell segments are spread apart radially by engagement of their rear ends with the taper of the annular collar. When the insertion force of the bolt is released, the O-ring urges the shell segments together to engage the threads of the bolt so that the nut can be tightened on the bolt. As the shell assembly only has to be moved at most the displacement distance xe2x80x9cxcex4xe2x80x9d to bring the external surfaces thereof in abutment with the internal front surface of the nut casing, the nut can be tightened (preloaded) with a relatively few number of turns N equal to xcex4/p, or h/(pxc3x97tan(xcex1/2)).
In other embodiments, the spring member may be formed integrally with the end retainer. For example, it may be a wave compression spring, a segmented spring, circumferential or axial leaf springs, or a flexure spring attached to the end retainer. The shell segments, spring member and end retainer may also be configured to cooperate with an external sleeve member for pulling the shell assembly back relative to the nut casing for quick disengagement from the fastener. Radial, axial, or flat surfaced key elements may also be provided between the nut casing and the shell segments to prevent relative rotation between the parts when the fastener is subjected to preloading forces.